1. Field of the Invention
The invention is related to plasma-assisted, low temperature conversion of coal in the presence of a light hydrocarbon to produce liquid hydrocarbons that are subsequently upgraded to liquid transportation fuels. The fuel conversion can be designed to produce liquid transportation fuels in CO2 neutral processes.
2. Description of the Related Art
A pyrolysis process is the low temperature heating of coal in the absence of an external supply of oxygen. The heating of coal causes devolatilization and produces a mixture of light gases, tar oils and char. Pyrolysis is usually carried out at low temperatures as compared to gasification to maximize the yield of tar oils. The pyrolysis liquids (called pyro-oils) composition depends on a number of factors such as temperature, residence time, pressure, heating rate, etc. The liquids generated from pyrolysis are generally low in quality and need considerable upgrading to remove aromatics and increase hydrogen composition.
Hydro-liquifaction is similar to pyrolysis process generating liquid fuels from coal. The hydro-liquifaction requires hydrogen as feed to this exothermic process. The drawback of this process is that the liquid yield is low and the liquids are high in aromatics and require significant upgrading to be sold as liquid transportation fuels. Also, natural gas reforming is done to produce hydrogen, which produces CO2. The heat required for the reforming process is provided by burning the char. This further increases the production of CO2.
Hydro-gasification is carried out at higher temperatures. This process has been developed specifically to make methane from coal at high temperatures. The process, if carried out at lower temperatures, can increase the yield to liquids. It suffers from the same disadvantages as pyrolysis and hydro-liquifaction in that the liquids created require significant upgrading and the hydrogen needed to upgrade the liquids creates excess CO2 emissions.
All these approaches use combustion of valuable char as source heat. Thus, they all produce CO2 from char combustion. In addition, CO2 is produced in the reforming process by converting natural gas to hydrogen and CO2. Therefore, it would be desirable to provide a process that does not require the combustion of char, is CO2 free, the hydrogen required for fuel upgrade is provided by natural gas, and the energy required for the process is provided by a renewable energy.